OK...heres the story. A while back my huge angel died (like 2 years ago). Back then I had a very pretty planted tank with an angel, couple of bleeding hearts, cherry barbs, and some otos (3-6 not sure how many). So after it died I bought a male pink convict, and decided to get another convict after a while. They bred and the pink male went psycho and killed everything, Including his mate. Buuut the babies lived and I took them to the pet store where I say a big jack dempsey being kept in a 10g tank. So I saved it and put it in the (still too small but bigger than 10) 29g tank. Well, it and the convict tor my tank apart over a span of about a year, and now its ugly.
So now I want to remodel. I plan to move the convict and give away to dempsey to a bigger and better home. I want to start the 29g from scratch, and make a nice peaceful community. Heres my current Ideas:

first idea: about 10 neons; about 5 serpaes; some otos; and a rainbow fish as the center peace/fish and maybe soemthing else

I'd go with number three. Of course, that's pretty much what I have in one of my own tanks! A powder blue or fire red dwarf gourami looks nice in a tank with neons or cardinals, and the serpaes too. Give them some tall thin plants to swim around in, and a fair amount of rocks for hiding/dithering places. The size of the gourami will keep the neons schooled up, but not stress them out.
Tiger Barbs can be too aggressive for neons, they sometimes bully them to death.

Be careful with the serpaes and neons together. I know some people have kept them successfully; I had to do an emergency re-home of my serpaes when they shredded my neons. It all depends on the individual fish, so just watch to make sure all is well when they are introduced.

Rainbow fish are more schooling fish, so I wouldnt recommend them alone. Also, at minimum, it should be 1 male, 1 female, since the male won't colour up fully without a female present, and females are usually very dull

I've never had rainbows in my tanks, but I have had gouramis. I didn't want to speak to something I didn't know about, but I do know how the gouramis will behave with neons, cardinals, serpaes, plus with black tetras, bloodfins, and red phantom tetras.,And how they'll behave with gouramis.
My grourami was part of a pair that I got from a friend. They decided they didn't like each other anymore after the move, so he had to move out. Everybody in that tank gets along just fine, but the female is still aggressive.